And an email from a manager at an unnamed hospital in the South West revealed three locums are refusing to work unless their pay is increased by 56 per cent.

Health Secretary Jeremy Hunt imposed a pay cap for locum doctors and nurses in 2015 of up to 55 per cent more than the rates paid to permanent staff members.

But hospitals often ignore this and offer far higher rates as otherwise locums might not work, which could leave them short-staffed.

Mr Mackey said: ‘We are trying to hold our nerve and not blink, but safety will drive the decisions. Behaviour reported by trusts in recent days suggested a number of medics were working together, to collectively withdraw labour in an effective “strike”. I don’t know how they’re on the register.’

One unnamed NHS finance director told the HSJ the locums’ tactics were like a ‘Mexican standoff’.